The present invention is directed to an attachment member, including a fastening element, such as a nail, to be driven into hard receiving materials by an explosive powder charge operated setting tool, and a prestressing element. The nail has an axially extending shank with a tip at its leading end and with the prestressing element laterally enclosing at least the tip. The prestressing element has an axially extending sleeve portion and a flange-like contact part at the leading end of the sleeve portion.
Attachment members of the above type used with an explosive powder charge setting tool are preferably selected for mass production. Such attachment members are used to fasten parts such as cable conduits, cable clips, cable clamps, insulation panels, suspensions and the like. These parts are secured to hard receiving materials such as concrete, masonry, rock, steel and the like.
In anchoring the above mentioned fastening elements, a nail, bolt or similar member is driven into the hard receiving material by an explosive powder charge operated setting tool. The fastening element is laterally enclosed by a prestressing element which bears against the receiving material or against the part to be fastened to the receiving material. A load engagement means on the fastening element is displaced into contact with the prestressing element at the completion of the driving operation, with the load engagement means being in the form of a head, a collar, a threaded nut or the like.
The parts to be secured by the attachment member are formed mostly of plastics material for economic considerations and also in specific cases for purposes of insulation. The use of the plastics material for the parts to be attached results in certain problems when the attachment is effected by explosive powder charged operated setting tools. It must be assured that the part being attached is sufficiently held or clamped against the receiving material. This requires a definite setting depth of the fastening element so that on one hand there is no danger of insufficient clamping and on the other hand there is no danger of destruction to the parts being secured.
When explosive powder charge operated setting tools are used, it is difficult to obtain a precise setting depth of the fastening element. This occurs due to the lack of homogeneity of the receiving material and also because of the variations in the energy supplied by the propellant or explosive powder charges. If the fastening element does not penetrate sufficiently into the receiving material, the part to be attached is not effectively clamped against the receiving material. On the other hand, if the fastening element penetrates too deeply into the receiving material, there is the danger that the part being attached may be destroyed.
To avoid destruction of brittle materials, an attachment member is known from DE-PS 16 25 367 made up of a fastening element and a prestressing element. The prestressing element has a flange-like contact part at its leading end, and a sleeve part extending from it opposite to the driving direction.
In this known attachment member the leading end face of the flange-like contact part is larger than the transverse cross-sectional surface of the fastening element by only a limited amount. As a result, there is a considerable area pressure acting during the driving operation on the receiving material. Such pressure causes spalling to take place in brittle materials and such spalling has a negative effect on the quality of the attachment and also there is a poor appearance of the attachment. Moreover, there is a considerable danger that the explosive powder charge operated setting tool, may be tilted when it is placed against the receiving material, whereby the fastening element does not enter the receiving material in a perpendicular position. In addition, the bolt guidance in the explosive powder charge operated setting material requires an expensive and cumbersome construction to guarantee the guidance of the fastening element during the driving operation.